Device for tightening and sealing plastic packaging straps

ABSTRACT

The device according to the invention for tensioning and sealing plastic strapping bands for packages has a housing ( 11 ), a band channel ( 14 ) extending in the longitudinal direction of the strapping band ( 12 ), which is open on one side and which receives the band ends ( 19,20 ), which channel is limited on one of its side by a tensioning plate ( 16 ) and on its other side by a tensioning wheel ( 18 ) provided with a profiling, whereby the tensioning wheel and the tensioning plate can be abutted relatively to one another. So as to be able to exert a large tensioning force on the band ends even with a small abutment force between the tensioning wheel and the tensioning plate, without damaging the band by rotating the tensioning wheel, it is suggested by the invention that the profiling consists of first transverse profile grooves ( 27 ) running approximately in the axial direction of the tensioning wheel and of second circumferential profile grooves ( 29 ) running in the circumferential direction, whereby the transverse profile grooves comprise a smaller slot depth than the circumferential profile grooves. Tensioning teeth ( 30 ) are formed at the circumference of the tensioning wheel by this arrangement, which teeth penetrate up to the depth of the transverse profile grooves into the band even with a small abutment force between tensioning plate and tensioning wheel, and ensure a transfer of high tensioning forces.

[0001] This invention relates to a device for tensioning and closing plastics strapping bands for packages or the like, with a housing, a band channel extending in the housing in the longitudinal direction of the housing of the strapping band, and which band channel receives the band ends of the strapping band which are to be tensioned mutually, which channel is limited on one side by a tensioning plate and on its other side by a tensioning wheel provided with a profiling, in which the tensioning wheel and the tensioning plate can be abutted relatively to one another.

[0002] Devices of this type serve to tension the band ends of plastic bands placed around packages against one another and to connect them firmly by means of a sealing device, so that the packages are securely strapped afterwards. For this, the band ends of the plastic strapping band are inserted into the band channel which is open on one side in such a manner that they lie on top of one another. Subsequently, the tensioning wheel and the tensioning plate are abutted relatively to one another, so that one band end abuts the tensioning plate firmly, and the other band end abuts the tensioning wheel, which is then rotated by hand or by a motor and tensions the band end abutting it with regard to the band end which is held by the tensioning plate. When the desired tension is reached, the band ends are connected firmly to one another by means of a friction welding device or different sealing devices.

[0003] So as to achieve a tensioning of the strapping band which is as firm as possible, it is necessary to ensure a friction coefficient between the plastic band ends and the tensioning plate on the one hand and the tensioning wheel on the other hand, which is as high as possible. For this, at least the tensioning wheel has been provided with a profiling in the state of the art which consists for example of grooves running diagonally over the circumferential surface of the tensioning wheel, into which the plastic material of the one band end presses during the abutment of the tensioning wheel and the tensioning plate against one another, and is thereby held and tensioned better than by a smooth tensioning wheel. All known profilings have the common disadvantage that they are quickly clogged with plastic material, which is then chafed from the respective band end when the adhering friction between the tensioning wheel and the plastic band is exceeded and the tensioning wheel rotates on the plastic band. The friction necessary for the tensioning can then not be reached with such a tensioning wheel with added plastic material; furthermore the plastic band is weakened due to the wear of friction lifted from the rotating tensioning wheel and it can result that the strapping band tears near its sealing location in an undesired manner.

[0004] It is the object of the invention to create a device of the of the above-mentioned type, with which it is possible to exert a very high tensioning force onto the band without damaging the band by excessive chafing.

[0005] This object is solved by means of the invention in that the profiling consists of first transverse profile grooves running approximately in the axial direction of the tensioning wheel and of second circumferential profile grooves running in the circumferential direction, whereby the transverse profile grooves comprise a smaller slot depth than the circumferential profile grooves. Thereby, the profile grooves preferably have a V-shaped or trapezoidal cross section which tapers towards the groove base lying radially inwards. It has proved to be particularly advantageous if the circumferential profile grooves have a V-shaped cross section and the transverse profile grooves have a trapezoidal cross section tapering towards the groove base lying radially inwards.

[0006] The circumferential and/or transverse profile grooves thus form approximately pyramidal pointed tensioning teeth between them, which can easily penetrate the band end which is to be tensioned, even with a small pressure force and which can grasp these with a positive fit and tension them. The transferable traction forces which are already large with a small pressure force between the tensioning wheel and the tensioning plate enable a firm tensioning of the band ends against one another, without resulting in rotation of the tensioning wheel on the corresponding band end, so that no plastic material is cleared away from the band end, which softens with the devices known up to now due to the friction heat which occurs due to the sliding through of the tensioning wheel on the band end and settles in the profiling in such a manner, from which it could only be removed with great difficulty after cooling and hardening.

[0007] The low depth of the transverse profile grooves compared to the circumferential profile grooves ensures that the tensioning teeth cannot exit from below the band end which abuts the tensioning wheel and engage the other band end. For this, the transverse profile grooves preferably have a slot depth which is smaller than the thickness of the thinnest strapping band to be processed.

[0008] It is particularly advantageous if the tip angle of the tensioning teeth which is enclosed by the groove walls of the profile grooves is smaller than 60°, in particular between 35 and 45°, because, with such a small tip angle, a complete penetration of the tensioning teeth into the band is already achieved with a very small pressure force. The slot depth of the circumferential profile grooves is preferably 1.5 to 3 times of the slot depth of the transverse profile grooves. The slot depth of the transverse profile grooves can for example be between 0.2 and 0.4 mm, and the slot depth of the circumferential profile grooves can be between 0.6 and 1 mm.

[0009] A particularly advantageous embodiment results when the tensioning plate is also provided with holding teeth running in the longitudinal direction of the band channel, which engage the circumferential profile grooves in the tensioning position of the tensioning plate and the tensioning wheel a bit when the band is not inserted. The holding teeth of the tensioning plate and the circumferential profile grooves of the tensioning wheel are then slightly crossed with one another whereby one can work with even smaller pressure forces between the tensioning plate and the tensioning wheel so as to introduce the desired high traction forces into the band ends and to tension these very firmly against one another.

[0010] The device is preferably provided with a sealing mechanism guiding the tensioning wheel in the tensioning position relative to the tensioning plate in the axial direction of the tensioning wheel, which mechanism consists for example essentially of a guide finger projecting from the tensioning plate engaging a guide slot circulating in the circumferential direction in the tensioning wheel. With the sealing mechanism it is ensured that the floatingly arranged tensioning wheel always takes exactly the correct axial position relative to the tensioning plate and that the tensioning teeth of the tensioning wheel cannot collide with the holding teeth of the tensioning plate, but cleanly engage the grooves formed between the holding teeth. It is particularly advantageous if the guide finger abuts the guide slot base of the guide slot with its free end in the tensioning position when the band is not inserted, so that the tensioning teeth of the tensioning wheel cannot come into immediate contact with the tensioning plate when the band is not inserted, which otherwise could lead to damages. So as to ensure an easy safe engagement of the guide finger in the guide slot, this preferably forms a centring guide for the guide finger in its radially outwardly lying region.

[0011] The arrangement of transverse profile grooves and circumferential profile grooves with different depths according to the invention enables in a particularly advantageous advancement of the invention also the use of a cleansing device which is assigned to the tensioning wheel for the profile grooves. This advantageously consists essentially of a cleansing block with cleansing teeth which engage the profile grooves. During the rotation of the tensioning wheel, the cleansing teeth peel out contaminations from the circumferential profile grooves, whereby a particularly thorough cleansing can be achieved in that the cleansing teeth reach the slot base of the circumferential profile grooves with their tooth tips. It has also surprisingly been shown that contaminations in the transverse profile grooves are carried out without problems, as these generally adhere to the plastic or other particles which have settled in the circumferential profile grooves. In particular with a trapezoidal arrangement of the transverse profile grooves, the dirt particles settling therein are removed again without any problems during the scraping of the circumferential profile grooves by means of the cleansing device.

[0012] The cleansing device can abut the tensioning wheel under the action of a pressure spring and thereby clean this permanently; but it is also possible to operate the cleansing device only when necessary or at regular intervals. A particularly advantageous arrangement results when the cleansing block is formed approximately wedge-shaped and abuts the tensioning wheel with a free wedge edge, whereby the unimpeded removal of the dirt particles removed from the grooves is ensured. It is particularly advantageous if the cleansing block consists of a soft metal, in particular a brass alloy, which leads to a self-sharpening effect when the cleansing block is pressed against the tensioning wheel. The cleansing teeth which engage the circumferential profile grooves are thereby optimally adapted to their form and scrape the profile grooves safely and completely.

[0013] Further characteristics and advantages of the invention result from the following description and the drawing, in which a preferred embodiment of the invention is explained in further detail by means of an example. It shows:

[0014]FIG. 1 a device according to the invention for tensioning and sealing of plastic strapping bands in a side view, whereby the housing of the device is merely suggested;

[0015]FIG. 2 a section through the tensioning wheel and the tensioning plate of the device represented in FIG. 1 in the region of the band channel with the strapping band not inserted;

[0016]FIG. 3 the object of FIG. 2 with the inserted strapping band;

[0017]FIG. 4 a detail of the tensioning wheel in the region of the cleansing block cooperating therewith in an enlarged section IV according to FIG. 1.

[0018] The device 10 shown in FIG. 1, the housing 11 of which is shown with dots for a clearer representation, serves for tensioning and sealing a plastic strapping band 12, which is to be placed around a package or the like.

[0019] For this, the device 10 comprises a band channel 14 which extends in the longitudinal direction of the strapping band 12 in the housing, is open on one side, which is limited by a tensioning plate 16 at its bottom side 15 and by a tensioning wheel 18 at its upper side, and into which the two band ends 19, 20 of the strapping bands 12 are inserted from the open longitudinal side, as is known per se. The tensioning wheel 18 can abut against the stationary tensioning plate 16 with an eccentric drive 21 in a manner not explained in detail for tensioning the band ends 19, 20 against one another, so that the two band ends 19,20 are clamped between the tensioning plate 16 and the tensioning wheel 18, whereupon the drive 22 for the tensioning wheel is operated, which then draws the upper band end 19 backwards into the device 10, in the drawing to the right, while the lower band end 20 is held in its position by the tensioning plate 16. When the desired tension in the strapping band 12 is reached, the friction welding device 23 arranged in the longitudinal direction of the strapping band behind the tensioning wheel is operated, which chafes the upper band end 19 in a known manner transversely to the longitudinal direction of the band with a high velocity over the lower band end and thereby produces a firm weld connection of the two band ends.

[0020] So as to achieve a large tension in the strapping band 12 between the tensioning wheel and the tensioning plate and the band ends lying therebetween even with small pressure forces, the tensioning wheel 18 is provided with a profiling 25 at its circumference, the arrangement of which can be seen in FIGS. 2 to 4. The profiling 25 consists of first transverse profile grooves 27 running in the axial direction 26 of the tensioning wheel 18, and of second circumferential profile grooves 29 running right-angled thereto in the circumferential direction 28, which have a larger slot depth T than the transverse profile grooves. In the depicted example of the embodiment, the slot depth T of the circumferential profile grooves is about 0.7 mm, while the slot depth t of the transverse profile grooves is only at 0.3 mm. FIGS. 2 to 4 further show that the circumferential profile grooves have an approximately V-shaped cross section and are close to one another, while the transverse profile grooves are formed with a trapezoidal cross section. The circumferential and transverse profile grooves 27, 29 which are next to one another or behind one another form pointed tensioning teeth 30 between them which are approximately pyramidal, the angle α, which is enclosed by the groove walls 31 of the profile grooves being about 40°.

[0021] As can easily be seen from FIG. 3, the tensioning teeth 30 gently press into the upper band end 19 up to a depth t of the transverse profile grooves 27 and already provide a practically positive-fit connection between its profiling 25 and the upper band end with a small pressure force. The maximum penetration depth which is determined by the slot depth t of the transverse profile grooves ensures that the tensioning teeth 30 do not exit again at the bottom side of the upper band end 19, as the thickness D of the strapping band is regularly higher than 0.3 mm. Thus, it cannot result that the tensioning teeth 30 of the tensioning wheel are pressed into the lower band end through the upper band end which would make a tensioning of the two parts against each other impossible.

[0022] As results further from the drawings, the tensioning plate 16 is provided with holding teeth 32 running in the longitudinal direction of the band channel 14, which engage the circumferential profile grooves 29 a bit in the tensioning position of the tensioning plate 16 and the tensioning wheel 18 when the band is not inserted as in FIG. 2. The holding teeth 32 provide that the lower band end 20 is also held firmly in that band channel during the tensioning process, in that the holding teeth 32 press into the lower band end from underneath, as the tensioning teeth 30 of the tensioning wheel 18 do from the upper side in the upper band end 19. The particular arrangement of the holding teeth and the tensioning teeth relatively to one another, in which the holding teeth project a bit into the circumferential profile grooves, and correspondingly the tensioning teeth into the holding grooves 33 which are formed between the holding teeth, when no strapping band is inserted between the tensioning plate and the tensioning wheel, ensures a tractive force which is exerted on the band ends which is as high as possible with small pressure forces between the tensioning wheel and the tensioning plate. As the tensioning teeth or the holding teeth press firmly into the band ends from above or below even with little pressure, there does not result a rotating of the tensioning wheel at the upper side of the upper band end or a drawing of the lower band end over the tensioning plate, so that the band ends are not damaged during the tensioning and that no or only very little abrasion is produced during the tensioning which could clog the profile grooves or the holding grooves.

[0023] So as to keep the profile grooves 27,29 free from this small abrasion or from dirt particles which can enter the device, the device 10 is provided with a cleansing device 34 above the band channel 14 for the tensioning wheel 18, which essentially consists of an approximately wedge-shaped cleansing block 35 which is provided with cleansing teeth 37 at its free front wedge edge 36 which engage the circumferential profile grooves 29. The arrangement is made in such a manner that the cleansing teeth 37 reach the slot base 39 of the circumferential profile grooves with their tooth tips 38.

[0024] The cleansing block 35 is pivotally mounted at an axis 40 and is pressed to the tensioning wheel 18 with its free wedge edge 36 by a pressure spring 41, whereby the cleansing teeth press firmly into the circumferential profile grooves 29 with their tooth tips and scrape out contaminations which have accumulated in the circumferential profile grooves during the rotation of the tensioning wheel. It has been shown that contaminations which have accumulated in the transverse profile grooves 27 are also slugged out, as these grooves only have a small slot depth, and furthermore the trapezoidal form of the profile grooves easily prevents a fast settling of contaminations therein. The cleansing block consists of a softer material than the tensioning wheel 18 or its tensioning teeth, in the present example of the embodiment of brass, so that its cleansing teeth 37 are continually ground during the rotation of the tensioning wheel and always engage the circumferential profile grooves exactly and without play, and also thereby scrape these out safely and completely.

[0025] While the tensioning teeth 30 of the tensioning wheel 18 engage the holding grooves 33 a bit, as is depicted in FIG. 2, the holding grooves are also freed from contaminations which possibly collect therein, when the tensioning wheel is rotated without a strapping band being inserted. So as to prevent that the tensioning teeth and the holding teeth collide or so as to avoid that the tips of the tensioning teeth 30 touch the slot base of the holding grooves 33 and can be damaged thereby, the device 10 comprises a sealing mechanism 42 which guides the tensioning wheel 18 in the tensioning position relative to the tensioning plate in the axial direction 26 of the tensioning wheel, which mechanism essentially consists of a guide finger 43 projecting from the tensioning plate 16, which engages a guide slot 44 circulating in the circumferential direction 28 in the tensioning wheel 18. The arrangement is chosen in such a manner that the guide finger 43 abuts the guide slot base 46 in the tensioning position of the tensioning wheel and the tensioning plate, whereby the tips of the tensioning teeth 30 still engage between the holding teeth 32, but are held with a sufficiently large distance from the slot base of the holding grooves 33. The guide slot 44 passes over into the circumferential surface of the tensioning wheel 18 in its region which is lying radially outwards and thus forms a centring guide 47 for the guide finger 43 which ensures that the floatingly mounted tensioning wheel always reaches the exact engagement with the guide finger 43 during the abutment against the tensioning plate with its guide groove 44. 

1. Device for tightening and closing plastic strapping bands for packages or the like, having a housing, a band channel extending in the longitudinal direction of the strapping band in the housing, which is open on one side and which receives the opposed band ends of the strapping band which are to be tensioned mutually, which channel is limited on one side by a tensioning plate and on the other side by a tensioning wheel provided with a profiling, whereby the tensioning wheel and the tensioning plate can be abutted relatively to one another, characterised in that the profiling (25) consists of first transverse profile grooves (27) running approximately in the axial direction (26) of the tensioning wheel (18) and of second circumferential profile grooves (29) running in the circumferential direction, whereby the transverse profile grooves (27) comprise a smaller slot depth (t) than the circumferential profile grooves (29).
 2. Device according to claim 1, characterised in that the circumferential profile grooves (29) and/or the transverse profile grooves (27) have an approximately V-shaped or trapezoidal cross section which tapers towards the groove base lying radially inwards.
 3. Device according to claim 1 or 2, characterised in that the circumferential profile grooves (29) have a V-shaped cross section, and the transverse profile grooves (27) have a trapezoidal cross section which tapers towards the groove base (37) lying radially inwards.
 4. Device according to one of claims 1 to 3, characterised in that the circumferential and/or transverse profile grooves (29 or 27) form approximately pyramidal pointed tensioning teeth (30) between each other.
 5. Device according to one of claims 1 to 4, characterised in that the transverse profile grooves (27) have a slot depth which is smaller than the thickness (D) of the thinnest strapping band (12) to be processed.
 6. Device according to one of claims 1 to 5, characterised in that the tip angle (α) of the tensioning teeth which is enclosed by the groove walls (31) of the profile grooves (27,29) of the tensioning teeth (30) is smaller than 60°.
 7. Device according to claim 6, characterised in that the tip angle (α) is between 35° and 45°.
 8. Device according to one of claims 1 to 7, characterised in that the slot depth (T) of the circumferential profile grooves (29) is about 1.5 to 3 times of the slot depth (t) of the transverse profile grooves (27).
 9. Device according to one of claims 1 to 8, characterised in that the slot depth (t) of the transverse profile grooves (27) is between 0.2 and 0.4 mm and the slot depth (T) of the circumferential profile grooves (29) is between 0.6 and 1 mm.
 10. Device according to one of claims 1 to 9, characterised in that the tensioning plate (16) is provided with holding teeth (32) running in the longitudinal direction of the band channel (14) which engage the into the circumferential profile grooves (29) in the tensioning position of the tensioning plate (16) and the tensioning wheel (18) a bit.
 11. Device according to one of claims 1 to 10, characterised by a sealing mechanism (42) guiding the tensioning wheel (18) in the tensioning position relative to the tensioning plate (16) in the axial direction (26) of the tensioning wheel.
 12. Device according to claim 11, characterised in that the sealing mechanism (42) essentially consists of a guide finger (43) projecting from the tensioning plate (16), engaging a circulating guide groove (44) in the tensioning wheel (18) in the circumferential direction (28).
 13. Device according to claim 12, characterised in that the guide finger (43) abuts the guide groove base (46) of the guide groove (44) with its free end (45) in the tensioning position when the band is not inserted.
 14. Device according to one of claims 1 to 13, characterised in that the guide groove (44) forms a centring guide (47) for the guide finger (43) in its radial outward region.
 15. Device according to one of claims 1 to 14, characterised by a cleansing device (34) assigned to the tensioning wheel (18) for the profile grooves (27,29).
 16. Device according to one of claims 1 to 15, characterised in that the cleansing device (34) essentially consists of a cleansing block (35) having cleansing teeth (37) which engage the circumferential profile grooves (29).
 17. Device according to one of claims 1 to 16, characterised in that the cleansing teeth (37) reach the bottom of the groove (39) of the circumferential profile grooves (29).
 18. Device according to one of claims 1 to 17, characterised in that the cleansing device (34) abuts the tensioning wheel (18) under the action of a pressure spring (41).
 19. Device according to one of claims 1 to 18, characterized in that the cleansing block (35) is approximately wedge-shaped and abuts the tensioning wheel (18) with its free wedge edge (36).
 20. Device according to one of claims 1 to 19, characterised in that the cleansing block (35) consists of a soft material, in particular of brass alloy. 